Photopolymerization-induced phase separation of the constituent components in holographic polymer-dispersed liquid crystals (H-PDLCs) causes a huge variation of the refractive index for light as well as for neutrons. We demonstrated that H-PDLCs with the thickness of only 30 micrometers act as extremely efficient gratings for neutrons. The lightinduced refractive-index modulation for neutrons of about 10-6 was observed, which is nearly two orders of magnitude larger than found in the best photo-neutron-refractive materials probed up to now. This makes H-PDLCs very promising candidate for fabricating neutron-optical devices.